Analysis of an efficient single-mode fiber coupler for all-fiber rotational Raman lidar

Consider comprehensively alignment errors and the central obstacle, an expression of coupling efficiency based on free-space optical coupling is derived, then the influence of these factors on coupling efficiency is numerically evaluated. An efficient single-mode fiber coupler with a graded-index lens is tailor-made and optimized for Raman lidar using optical software. Simulation results show that this optimized coupling scheme may make the coupling efficiency to increase by 44.5% for Gaussian beam than without a graded-index lens if lidar returning signals parallel to optical axial is only considered, and that the multi-core fiber may redouble the optical energy coupled into all-fiber spectroscope.